Solenoid-actuated valves are used in many applications, including but not limited to fuel vapor control. It may be desirable to monitor the movement of an armature as it moves between the closed and open positions when the solenoid coil is energized by an actuating voltage across the coil. Typically, the armature begins to move after the current in the coil builds up to a sufficient level. The armature then moves until it reaches an end point where it comes to a full stop in an open position.
To monitor the motion of the solenoid, there are circuits that detect when the valve is either open or closed by detecting discontinuities in the current signature of the coil current. More particularly, the current signature has a significant discontinuity (e.g., a sharp dip in the current level) when the armature reaches a fully open position and a similar discontinuity when the armature reaches a fully closed position. Currently known monitoring methods compare the actual current signature and a predetermined current signature between time values corresponding to the end points, or hard stops, in the armature travel path.
Although existing methods can determine whether a valve is functioning properly by measuring the current and the elapsed time between the hard stops, there is currently no way to detect when the valve begins to open (i.e., “cracks” open) because there may a delay between the time the coil is energized and the time the armature begins to open the valve due to, for example, the time required to build sufficient current to move the armature and/or to take up any lash in the armature. In other words, existing methods only detect the hard stops in the armature movement, not any subtle movements of the armature between the two hard stops. As a result, there is no way to accurately determine the time period during which the armature is actually moving, making it difficult to pinpoint how long the valve is actually open during a given energization cycle.
There is a desire for a method that can accurately detect when the valve cracks open as well as when the valve is fully open to provide additional information that may be used to, for example, improve operation in a fuel vapor control system or enhance the diagnostic capabilities of the system in which the valve operates.